The keys to revision total knee arthroplasty start with understanding the nature of the problem. Revision TKR is a major undertaking and should be focused on problem solving. Know the problem and remember pain is not a diagnosis. Review history of the problem and think of the possibilities: infection, loosening, instability, stiffness, malalignment, and poor kinematics.

Ensure an adequate workup including an adequate history, exam and imaging including radiographs, MRI for soft tissue issues, and CT scans to assess rotational alignment. Labs should include CBC, ESR, C-reactive protein, and an aspiration including cell count and culture.

Synthesise a working diagnosis and formulate a provisional plan to include what is to be revised, how will you get there remembering old incisions, and how will get the parts out? Think about equipment: what tools do you need and implant specific tools.

Finally, once everything is out, think about what you have left (soft tissue defects and bone defects) to “rebuild”? This involves pondering constraint for soft tissue defects, stems for mechanical stability, cones, augments, bone graft for osseous defects and fixation.

Following a careful in-depth preoperative plan for revision TKA, the first surgical step is adequate exposure. It is crucial to plan your exposure for all contingencies. Prior incisions have tremendous implications and care must be taken to consider their impact. Due to the medially based vascular supply to the skin and superficial tissues about the knee, consideration for use of the most LATERAL incision should be made. It is essential to avoid the development of flaps which may compromise the skin and soft tissue which can have profound implications.

Exposure options can be broken down into either PROXIMALLY based techniques or DISTALLY based options. The proximal based techniques involve a medial parapatella arthrotomy followed by the establishment of medial and lateral gutters. An assessment of the ability to evert or subluxate the patella should be made. Care must be taken to protect the insertion of the patella tendon into the tibial tubercle. If the patella is unable to be mobilised, then extension of arthrotomy proximal is performed. If this is not adequate, then consider inside out lateral release. If still unable to mobilise, then a QUAD SNIP is performed. In rare instances, you can connect the lateral release with quad snip resulting in a V-Y quadplasty, which results in excellent exposure.

Another option is to employ DISTALLY based techniques such as the tibial tubercle osteotomy technique described by Whiteside. A roughly 8cm osteotomy segment with distal bevel is performed. The osteotomy must be at least 1.5–2cm thick: too thin and risk of fracture increases. This approach leaves the lateral soft tissues intact and then a “greenstick” of the lateral cortex is performed with eversion of patella and the lateral sleeve of tissue. This technique is excellent for not only exposure but also in instances where tibial cement or a cementless tibial stem needs to be removed. Closure is accomplished with wires either through the canal or around the posterior cortex of the tibia.

First generation condylar knee replacements suffered from 2 prominent observations: Difficulty in stair climbing and Limited range of motion.

Improved understanding of knee kinematics, the importance of femoral rollback, and enhanced stability in flexion led to 2 differing schools of thought: posterior cruciate ligament retention or posterior cruciate substitution. The advantages of posterior cruciate substitution include predictable CAM-post engagement leading to rollback, predictable ROM, stability during stair climbing, ease of knee balancing regardless of degree of angular deformity, and avoidance of issues such as PCL tightness / laxity at time of index procedure, as well as late ligament disruption leading to late instability.

Evolution has shown that human appendages that no longer served a purpose, slowly shrivel up. As we have seen with the appendix, the coccyx, and the erector pili muscles, these vestigial organs no longer are necessary for daily function and are destined for obsolescence. I submit: the PCL in knee arthroplasty IS THE VESTIGIAL ORGAN: not the posterior stabilizing mechanism!

The interest in osteolysis has waned largely due to the impact of crosslinked polyethylene and the “rarity” of this phenomenon. However, the basic process still remains: particles, motion observed with unstable implants and host specific factors all play a role in bone loss around implants. There are 2 predominant patterns of lysis: Linear versus Expansile. Linear Lysis: is focal bone loss at the interface as seen in the bone cement interface in when using acrylic or at the implant-host interface with porous ingrowth/ongrowth implants. Expansile Lysis: is observed in less contained regions such as the retro- and supra-acetabular regions around the socket. These lesions can also be quite extensive yet may be subtle in appearance.

Imaging is essential in identifying the extent and magnitude of osteolysis. Available modalities include plain radiographs although they can be of limited value in that even with oblique views, they often underestimate the degree of bone loss. CT scans are useful but can be limited by artifact. Several centers have explored the role of MRI in assessing lysis. It can be useful for bone loss and provides excellent assessment for soft tissue: abductors, neurovascular structures. Metal artifact reduction sequencing is required to maximise information obtainable.

Management of osteolysis: Identification and monitoring periprosthetic osteolysis is a crucial element of patient care. Progressive bone loss leading to loss of fixation and the potential risk for periprosthetic fracture is a real possibility and early recognition and intervention is a priority. The basic Guiding Principles of management are centered around several key elements including the source of osteolysis and degree, the fixation of implant, the location of lysis, the track record of implant system, the presence of patient symptoms (if any), and finally the patient age, activity level, and general health.

Specifics of treatment of osteolysis around the acetabulum: With cemented sockets, lysis is typically seen late and frequently at the bone-cement interface. It is often associated with a loose implant and the prime indication for surgery may be pain. Treatment involves implant removal and revision with an uncemented cup and bone grafting or augmentation as needed.

With uncemented sockets in the setting of osteolysis, there are several factors to consider. These have been stratified by Rubash, Maloney, and Paprosky. The treatment of these sockets has been summarised as follows: for Type I and Type II with limited lysis, lesional treatment such as debridement and bone grafting with head and polyethylene exchange has been suggested. WATCH for impingement!!!! Graft defects via trap-doors can be performed but make the door big enough to graft. Small doors and grafting through screw holes is at best marginal. In instances of compromised locking mechanisms, consider cementing the liner into the shell.

For Type II and Type III implants, revision of the component is recommended. With the currently available cementless cup extraction tools, I rarely hesitate to remove a cup with moderate lysis and a broken locking mechanism: better access to lytic areas, better grafting achieved. CAVEAT #1: the disadvantage of implant removal is that it is clearly a bigger procedure and fixation of the new implant may be more difficult. Risks vs. rewards. CAVEAT #2: Socket revision in the setting of failed MOM implants has some unique “issues”. In the Vancouver series, almost 25% of the revision cups failed to achieve biologic fixation. As such, recommendation for using “enhanced” porous implants during revision seems prudent. Additionally, despite the use of larger diameter heads, instability rates remain high.

First generation condylar knee replacements suffered from two prominent observations: 1) Difficulty in stair climbing, 2) Limited range of motion (ROM).

Improved understanding of knee kinematics, the importance of femoral rollback, and enhanced stability in flexion led to 2 differing schools of thought: Posterior Cruciate ligament retention vs. Posterior Cruciate substitution. The advantages of posterior cruciate substitution include predictable cam-post engagement leading to rollback, predictable ROM, stability during stair climbing, ease of knee balancing regardless of degree of angular deformity, and avoidance of issues such as PCL tightness / laxity at time of index procedure, as well as late ligament disruption leading to late instability.

Evolution has shown that human appendages that no longer served a purpose, slowly shrivel up. As we have seen with the appendix, the coccyx, and the erector pili muscles, these vestigial organs no longer are necessary for daily function and are destined for obsolescence. I submit: the PCL in knee arthroplasty IS THE VESTIGIAL ORGAN: not the posterior stabilizing mechanism!

Understand the nature of the problem. Revision TKR is a major undertaking and should be focused on problem solving. Know the problem!- Pain is not a diagnosis. Review history of problem. Think of possibilities: Infection, loosening, instability, stiffness, malalignment, poor kinematics.

Ensure an adequate workup - History, Exam; Imaging: Radiographs: consider long alignment films, MR for soft tissue issues: Clunk, recurrent hemarthroses; CT scan: Remains gold standard for rotational alignment. Labs: CBC, ESR, C-reactive protein. Aspiration: Cell count, Culture.

Assessment of where the patient is currently!

Synthesise a working diagnosis and formulate a provisional plan. Revise “part of knee”: you better know what's in there! Revise “all of knee”.

How will you get there? Think old incisions

How will get the parts out? What tools do you need? High speed burrs / diamond tip wheel /long thin saw blades; Osteotomes; Implant specific tools.

Once everything is out: What do you have left? Soft tissue defects, Bone defects.

How to “rebuild”: Constraint for soft tissue defects, Stems for mechanical stability, Cones / augments / bone graft for osseous defects; Fixation: Cement, Cementless.

In 1998, lysis / wear were the biggest concerns in THR. 3 distinct tacks emerged: Alternatives to polyethylene: Ceramic / Ceramic; Metal / Metal; Make a better polyethylene

MOM story is well known: bad ending!!

Large adoption of Ceramic / Ceramic: positives: low wear, benign MR findings, even low dislocation rates !! negatives: fractures still occurred, noise generation, liner malseating, metal transfer (edge effects)

Crosslinked Polyethylene: Update: 13–15 year follow-up of 1st generation XLPE with remelted product: Annual wear rates of 0.004 (metal heads) 0.002 (ceramic heads)!

No lysis!! Wear rates for “standard” heads and large heads both low approaching the lower limits of detection!!

CONCLUSION: Crosslinked Polyethylene with Ceramic Heads: The Winner and Still Champion!

Longevity of total hip arthroplasty (THA) is dependent upon avoiding both short- and long-term problems. One of the most common short-term / early complications of THA is instability while longer term issues of wear remain a concern. Both of these concerns appear to be related to implant position: either static or functional. While achieving “ideal” implant position in primary THA for osteoarthritis is only successful in 50% of cases (Callanan et al.), it is even more difficult in complex primary disorders such as dysplasia and post-traumatic arthritis.

Many theories exist as to why implant position and short-term complications appear to be higher in this “complex primary” cohort but certainly the ability to achieve desired implant position appears to be more challenging. The loss of usual anatomic landmarks, the presence of soft tissue contractures, and the recognition of both pelvic and femoral deformities play a role.

Enabling technologies have emerged to help in achieving improved implant position. These technologies include both navigation (both imageless and image guided) as well as the newly adopted technology of robotic assistance. Robot-assisted THA is based upon a CT scan protocol. Three-dimensional pre-operative planning on both the femoral and acetabular side can be performed. Precision guided bone preparation and exacting implant delivery is achievable using robotic technology.

Examples of use of this technology in complex primary THA will be demonstrated including planning, preparation and implantation.

Introduction

Contemporary total knee systems accommodate for differential sizing between femoral and tibial components to allow surgeons to control soft tissue balancing and optimize rotation. One method some manufacturers use to allow differential sizing involves maintaining coronal articular congruency with a single radius of curvature throughout sizes while clipping the medial-lateral width, called a single coronal geometry system. Registry data show a 20% higher revision rate when the tibial component is smaller than the femur (downsizing) in the DePuy PFC system, a single coronal system, possibly from increased stresses from edge loading or varying articular congruency. We examined a different single coronal geometry knee system, Smith & Nephew Genesis II, to determine if edge loading is present in downsized tibial components by measuring area and location of deviation of the polyethylene articular surface damage.

Introduction

Robotically-assisted unicondylar knee arthroplasty (UKA) is intended to improve the precision with which the components are implanted, but the impact of alignment using this technique on subsequent polyethylene surface damage has not been determined. Therefore, we examined retrieved ultra-high-molecular-weight polyethylene UKA tibial inserts from patients who had either robotic-assisted UKA or UKA performed using conventional manual techniques and compared differences in polyethylene damage with differences in implant component alignment between the two groups. We aimed to answer the following questions: (1) Does robotic guidance improve UKA component position compared to manually implanted UKA? (2) Is polyethylene damage or edge loading less severe in patients who had robotically aligned UKA components? (3) Is polyethylene damage or edge loading less severe in patients with properly aligned UKA components?

Introduction

Cementless acetabular components are commonly used in primary and revision total hip arthroplasty, and most designs have been successful despite differences in the porous coating structure. Components with 2D titanium fiber mesh coating (FM) have demonstrated high survivorships up to 97% at 20 years¹. 3D tantalum porous coatings (TPC) have been introduced in an attempt to improve osseointegration and therefore implant fixation. Animal models showed good results with this new material one year after implantation², and clinical and radiographic studies have demonstrated satisfactory outcomes³. However, few retrieval studies exist evaluating in vivo bone ingrowth into TPC components in humans. We compared bone ingrowth between well-fixed FM and TPC retrieved acetabular shells using backscatter scanning electron microscopy (BSEM).

INTRODUCTION

Adverse local tissue reactions (ALTR) and elevated serum metal ion levels secondary to fretting and corrosion at head-neck junctions in modular total hip arthroplasty (THA) designs have raised concern in recent years. Factors implicated in these processes include trunnion geometry, head-trunnion material couple, femoral head diameter, head length, force of head impaction at the time of surgery, and length of implantation. Our understanding of fretting and corrosion in vivo is based largely on the analysis of retrieved prostheses explanted for reasons related to clinical failure. Little is known about the natural history of head-neck tapers in well-functioning total hip replacements. We identified ten well-functioning THA prostheses retrieved at autopsy. We sought to determine the pull-off strength required for disassembly and to characterize fretting and corrosion apparent at the head-neck junctions of THAs that had been functioning appropriately in vivo.

Following a careful in-depth preoperative plan for revision TKR, the first surgical step is adequate exposure. The following steps should be considered: 1.) Prior incisions: due to the medially based vascular supply to the skin and superficial tissues about the knee, consideration for use of the most LATERAL incision should be made. 2.) Avoid the use of flaps which may compromise the skin and soft tissue. 3.) Exposure options can be broken down into: PROXIMALLY based techniques: medial parapatella arthrotomy, establish medial and lateral gutters, eversion or subluxation of the patella, extension of arthrotomy proximal, if unable to “mobilise” patella, consider inside out lateral release, if still unable to mobilise: QUAD SNIP, in rare instances, connect lateral release with quad snip resulting in a V-Y quadplasty, may now turn down for excellent exposure.

DISTALLY based techniques: tibial tubercle osteotomy technique described by Whiteside, roughly 8 cm osteotomy segment with distal bevel, osteotomy must be at least 1.5–2 cm thick: too thin and risk of fracture increases, leave lateral soft tissues intact, greenstick” the lateral cortex with eversion of patella, closure with wires.

Periacetabular osteolysis is seen in response to particles (polyethylene, ceramic, metal or cement), at times in the presence of an unstable implant, and perhaps made worse by the unique host response to the particle burden. The impact of wear modes: due to either the primary bearing surface (MOP, MOM, COC) or unintended surfaces as seen in impingement, as well as the quality of the bearing counterface all influence the extent of the osteolytic response. The final common pathway appears to be via macrophage stimulation, an upregulation of cytokines leading to a resorption of bone.

The patterns of lysis range from linear resorption at the implant interface to more expansile patterns which can be more dramatic in size and may place the implant at jeopardy for loosening. Assessment of implant fixation as well as extent of the lytic process employs the use of plain radiographs (including oblique views), computerised tomography and magnetic resonance imaging. The utility of MRI for the quantification of bone loss as well as the newer phenomena of associated soft tissue lesions (pseudotumors, adverse tissue reactions) has turned out to be a valuable tool in helping determine timing and need for revision.

The basic principles in determining need for revision surgery revolve around: degree of lysis, integrity of the soft tissues, fixation of the implant, track record of the implant, as well as patient factors including symptoms, age and activity.

In cemented sockets, progressive bone loss, pain with or without overt loosening is indication for revision which is generally accomplished using an uncemented hemispherical acetabular component with bone graft and screw augmentation.

In the uncemented socket, the decision to revise is based upon a) implant stability, 2) the integrity of the locking mechanism, 3) degree of bone loss. With stable implants, polyethylene exchange and “lesional” treatment is appropriate. Well fixed implants with extensive lysis can be successfully managed with liner exchange and bone grafting as necessary. If the liner locking mechanism is compromised, cementing a liner into place is an excellent strategy. Removing a well fixed cup with extensive lysis runs the risk of encountering a large acetabular defect which may be difficult to reconstruct. Loose implants clearly require revision.

In the era of “hard bearings”, progressive soft tissue expansion leading to damage of the abductor and other soft tissue constraints about the hip is an indication for revision. Revision of MOM THR's may be performed by maintaining the femoral component and performing an isolated acetabular revision or in some instances of modular acetabular components, maintaining the shell and inserting a new liner. In all instances of implant retention, it is critical to confirm that the components are in optimised position: implants retained in suboptimal position are at risk for early failure.

Introduction

The longevity of total hip arthroplasty (THA) is dependent on acetabular component position. We measured the reliability and accuracy of a CT-based navigation system to achieve the intended acetabular component position and orientation using three dimensional imaging. The purpose of the current study was to determine if the CT-guided robotic navigation system could accurately achieve the desired acetabular component position (center of rotation (COR)) and orientation (inclination and anteversion). The postoperative orientation and location of the components was determined in 20 patients undergoing THA using CT images, the gold standard for acetabular component orientation.

Introduction

Implant position plays a major role in the mechanical stability of a total hip replacement. The standard modality for assessing hip component position postoperatively is a 2D anteroposterior radiograph, due to low radiation dose and low cost. Recently, the EOS® X-Ray Imaging Acquisition System has been developed as a new low-dose radiation system for measuring hip component position. EOS imaging can calculate 3D patient information from simultaneous frontal and lateral 2D radiographs of a standing patient without stitching or vertical distortion, and has been shown to be more reliable than conventional radiographs for measuring hip angles[1]. The purpose of this prospective study was to compare EOS imaging to computer tomography (CT) scans, which are the gold standard, to assess the reproducibility of hip angles.

Minimal or Less Invasive Approaches

Limited medial parapatellar incision – 2–3 inch medial incision; Best for unicompartmental implant; patellar visualization poor; Less invasive but limited visualization therefore overall joint inspection is compromised.

MIS TKR approaches - Mini midvastus approach popularised by S.B. Haas - Ideal BMI 30 or less; Incision length 10cm; Vastus incision about 2–3cm; Vastus incision beyond 5–6cm places motor branch to VMO at risk; Coupled with downsized cutting blocks, allows predictable ability to perform TKR; Sliding window concept; Patella eversion not necessary.

Mid Subvastus approach – 10cm skin incision; Sub vastus dissection up to septum (watch for bleeders!); VERY difficult in muscular males!

Standard Incisions

Standard medial parapatellar approach - Familiar to most surgeons; Medial arthrotomy facilitates exposure for almost all procedures; Can become more extensile by incising the quad tendon further proximal; Release of posteromedial capsule and semi-membraneosus allows exposure posteriorly.

Quad snip - Used occasionally in the fixed varus, flexion contracted knee; More commonly used in revisions; Allows patella eversion without risk of distal avulsion; Motor strength appears to return to baseline level postoperatively.

V-Y quadriceps turndown - Technique: initial medial parapatellar arthrotomy, an oblique tenotomy angled toward the tendinous portion of the vastus lateralis and then extended distally; The quadriceps segment is than retracted downward to expose the joint; Tenotomy is closed with robust non-absorbable sutures holding the knee in extension; Postoperative flexion is dictated by integrity of repair while flexing knee at time of closure. Disadvantages include extensor lag, as well as effecting ultimate ROM.

Tibial tubercle osteotomy a la Whiteside - Medial arthrotomy; Tubercle segment is 6–8cm long, 2cm wide and 1–1.5cm thick; Segment is beveled distally so as to avoid stress riser; Leave lateral soft tissue intact; Closure with wires preferred although screws or cables have been used as well.

Instability after total hip arthroplasty is the primary cause for revision surgery and is a frequent complication following revision surgery for any reason (Bozic et al, JBJS 2009). Surgical management of the unstable hip has not been uniformly successful with the best results occurring in those hips in which an identifiable cause of instability can be determined (Daly & Morrey, JBJS 1992). It was these sobering findings that led to the development of and increased use of constrained acetabular components.

While the results of revision surgery for instability using constrained components have been encouraging (Shapiro, Padgett, Sculco J Arthroplasty 2003) with a re-dislocation rate of less than 3%, reoperation for other reasons have noted to increase with time. The commonly used tripolar configuration has been susceptible to bearing damage at both the inner and outer bearing surface by the nature of the constrained mechanism (Shah, Padgett, Wright, J Arthroplasty 2009). In addition, we have noted instances of fixation failure directly related to the constrained acetabular device either from loss of implant fixation to the pelvis with or without cement (Yun, Padgett, Dorr, J Arthroplasty 2005).

The observation of these failure modes ranging from either fixation failures to overt biomaterial failure have led us to be extremely cautious in the “routine” use of constrained liners in revision THR.

Stratification of the recurrent dislocator has been nicely described by Wera et al (J Arthroplasty, 2012). The etiology of dislocation includes: acetabular malposition, femoral malposition, abductor deficiency, impingement, late bearing wear and unknown causes.

Implant instability due to malposition, impingement, and poly wear should be revised as appropriate to correct the underlying problem in addition to the use of either larger diameter heads. The emerging use of dual mobility articulations remains to be determined. However, the indiscriminate use of constrained liners should be avoided as the risk of problems outweighs their benefits.

Due to issues related to osteolysis which became increasingly evident in the 1990's, approaches to combat wear focused upon either improving ultra-high molecular grade polyethylene or to abandon it and employ alternative bearings: metal upon metal or ceramic upon ceramic (COC).

Ceramics have played a role in hip bearings for decades with much of the experience coming from Europe. While there is consistent evidence of low wear rates in this bearing couple due to its surface hardness, wettability and resultant low friction, problems unique to this bearing couple were noted: a small but real incidence of fracture, surface damage due to metal transfer and stripe wear as well as the unique issue of squeaking. What we have learned is that these hard bearings (either COC or Metal on Metal) despite being able to use larger diameter heads, are exquisitely sensitive to component position and orientation.

With the tremendous improvements in 2nd and now 3rd generation crosslinked polyethylenes demonstrating vastly reduced wear rates and having none of the issues of fracture, stripe wear, or squeaking, it remains unclear what role ceramic bearings have in modern use. Until the aforementioned issues are resolved, ceramic on ceramic bearings in the young patient should be used with caution. Ceramic-on-ceramic total hip arthroplasty: incidence of instability and noise.

Introduction

In total hip arthroplasty, the positioning of the acetabular cup, in particular, has been shown to play an important role in the survivorship of the prosthetic joint. The commonly accepted “safe zone” extends from 5–30° of anteversion to 30–50° of inclination. However, several studies have utilized a more restrictive safe zone of 5–25° of anteversion and 30–45° of inclination, a modification of the Lewinnek zone. Many attempts have been made to develop a more reliable method of positioning the acetabular component. Robotic-assisted surgery is one such method. The purpose of this study was to compare the resulting position of the acetabular component after robotic-assisted surgery with the intraoperative robotic data to determine if improved accuracy can be achieved with the robotic-assisted method.